1. Field of the Invention
The present invention relates to a light measuring device which can vary its light measuring range.
2. Description of the Prior Art
Existing TTL type of light measuring systems which receive light passing through a photographing lens and apply it to a photoelectric transducing element to measure the quantity of the object light. Also known are various kinds of mean light measurement system, including central preference means light measurement systems and partial light measurement systems. In other known light measurement systems means and partial light measurements can be carried out by two kinds of ligh beams. A camera which can change between mean and the partial light measurements has merit in that a desired exposure value can be obtained by an appropriate change. However, in most conventional devices, separate light measuring elements are used the mean and the partial light measurements and their outputs are switched. For example, the photoelectric element for the mean light measurement is arranged in the pentagonal prism view finder optics so as to carry out a mean or central preference light measurement of the object image on the focusing plate, while the photoelectric element for the partial light measurement is arranged mainly to measure the light at the central part of the picture via source optical means by changing between the outputs of the two photoelectric elements a proper exposure by the mean and the partial light measurement is calculated.
However, such conventional devices have the following inconveniences.
Two pieces valuable light sensing elements are needed. Also, two light measureing elements have to be arranged in the limited space of a camera.
Until now a device which can change between the partial and the mean light measurement with one light sensing element would carry out the switchover with a mechanical switch. This makes the mechanism complicated. This is inconvenient with reference to space and manufacturing cost.
Conventional devices also make it difficult to estimate light measurement with the output of the partial light measurement and that of the means light measurement when there is a need for backlight automatic compensation, daylight synchronization mode change over, and sky and ground backlight automatic compensation.
It is, accordingly, an object of the present invention to enable the change of the light measuring ranges by combining a light condensing member having more than two different optical characteristics with an electrooptical element.
Further, other features and objects of the present invention will become clear from the following description of embodiments of the invention when read in light of the accompanying drawings of the embodiments.